Wellington's popular waterfront diving platform was forced to close after faecal contamination spiked at nearly 500 times the safe level, documents reveal.

An email exchange issued under the Official Information Act showed that Wellington Waterfront and the city council decided to close the platform immediately on the Friday of the rugby sevens last year after getting advice from Regional Public Health.

But at the time, Wellington Waterfront chief executive Ian Pike pointed to drunken sevens fans as the main reason for the closure, with water quality mentioned only as contributing to the decision.

Yesterday, he said that was incorrect and while security guards were in place to stop drunken people taking a jump, the tournament was "coincidental" to the decision to close the platform.

It is not likely to reopen until March, when new baffles are installed to divert stormwater.

The documents showed that enterococci bacteria levels were well above 140cfu (colony forming units) per 100 millilitres of water, which is considered the safe level for swimming.

Anything over 280cfu is considered an unacceptable risk to health but Greater Wellington Regional Council recorded 69,000cfu on January 26 last year.

Wellington Waterfront was alerted to the spike on February 1, prompting Wellington medical officer of health Stephen Palmer to intervene.

"He says he feels compelled to close the dive platform immediately," an email from council spokesman Richard MacLean said.

An email from Mr Pike then stated that he had discussed the matter with Dr Palmer and they would close the platform that afternoon.

Yesterday, Dr Palmer said anything between 140cfu and 280cfu would spark extra monitoring but a level of 69,000cfu was "off the end of the scale".

"My advice was that the public should be warned of the danger . . . I don't think they quite understood the situation."

However, when The Dominion Post reported the closure on February 5, water quality was not the primary reason given.

Yesterday, Mr Pike said the safety of rugby fans had contributed to the decision to close the platform but "that was somewhat coincidental because the issue was about the water quality".

He could not say why he had pointed to the sevens as the reason at the time but said there were security concerns and the two events "overlapped each other".

Mr MacLean said there had been no attempt to downplay the seriousness of the contamination and there were legitimate concerns for sevens fans.

"The reason the sevens was brought into play was that there were reports of intoxicated people wearing strange outfits jumping into the water."

Signs were put up when the platform closed, advising of potential contamination in the water, he said.